One problem that urban planners can face is where to locate roads leading into, for example, a city core where traffic volume can be heavy. For example, it is not uncommon to provide a road, such as a highway, through or across the city core (often elevated above the city ground). The on and off ramps of such roads, however, can become bottlenecks to traffic flow—particularly at peak hours of usage, such as, for example, morning and evening rush hours.
Moreover, it is not uncommon for urban centres to be located near a body of water, such as, for example, a river, or lake, or other like body of water. Providing a road, such as a highway, through the city core often means running the road through the city's waterfront area. This can lessen the visual impact of the waterfront area. Moreover, the road can have a negative environmental impact on the waterfront area as well.